This invention relates to new and useful improvements in depth control means particularly adapted for use with agricultural implements such as cultivators, seed drills and discers and also with underground harvesters such as onion harvesters, sugar beet harvesters, potato harvesters, planters or seeders of the above as well.
It is well known, particularly in seeding operations, that the subsequent yield will be improved if the seed can be planted as close to the optimum depth as possible.
Under perfect conditions, of course, the seed can be placed the exact amount below the surface of the ground, but in actual practice, many factors affect the depth at which the seed is planted.
For example, uneven ground surface will cause the furrow openers to vary relative to the surface of the ground so that the seed will not be deposited at an even depth. When using relatively wide implements such as discers, the depth is maintained in part by the suction of the discs engaging the earth and if the density of the earth varies, then the suction will vary so that the depth at which the discs are working will also vary.
Furthermore, the seed boxes are usually mounted upon the implement and the weight acting upon the implement therefore varies as the seed quantity in the box varies once again affecting the depth of penetration of the furrow openers.
Also of importance in controlling the depth of penetration of the furrow opener, is the angle of inclination of the ground. For example, if working in one direction on a side hill, then the depth of penetration will be different than if the machine was working in the opposite direction or upon flat ground.
Some depth control devices utilize one or more wheels contacting the ground in advance of the implement, said wheels sensing the terrain and, in conjunction with other mechanism, controlling switches which increase or decrease the relative penetration of the earth working tools in order to maintain a preset depth.
These individual wheels suffer from several disadvantages, the principal one being that they tend to chatter or vibrate due to the unevenness of the terrain thus tripping the mechanism for depth control, when it is not really necessary to do so. Also, these wheels are sometimes difficult to steer when the implement is turned.